Title : Tunnel squeezing potential classification based on rock mechanics properties
Abstract:
Purpose: This study aims to evaluate the methods employed for classifying and quantifying the potential of squeezing in tunnels. Along with the empirical and semi?empirical approaches to anticipate the possible squeezing tunnel problems, the squeezing potential of the Karaj water transfer tunnel and North West Tunnel Convey (NWTC) tunnels (Lot 2), located in Iran, are evaluated and presented. Those two case studies have an interesting geology profile and parameters to identify and evaluate the squeezing potential.
Design/methodology/approach: In recent years, there has been an increasing interest in tunnel construction. This paper describes the squeezing behavior of poor rock mass associated with deformability and strength properties. The Karaj water transfer tunnel has eight lithological rock types; the NWTC tunnel (Lot2) has 21 Lithological rock types. The parameters for rock classification, such as rock quality designation (RQD), rock mass rating (RMR), modified RMR, Q?system, geological strength index (GSI), rock mass index (RMi), and rock structure rating (RSR), are evaluated and presented here. The above parameters are the input parameters for the squeezing study in Karaj and NWTC tunnels. According to different methods of squeezing evaluation of tunnel presented in tables, the results of two case studies are presented in this paper.
Findings: One of the more significant findings from this study showed that about 3 km of the second part of the NWTC tunnel and 2 km of the Karaj tunnel have high squeezing potential. This research deals with not only an overview of the methods used for the identifying and quantifying of squeezing along with the empirical and semi?empirical approaches presently available to anticipate the potential of squeezing tunnel problem, but also the case studies of NWTC and Karaj tunnels to evaluate and compare the potential of squeezing by different methods. These two tunnel case studies have a high possibility of squeezing; therefore, the lining of those two tunnels must be strong enough to overcome this issue.
Originality/value: This study is a precise and concise comparison of the evaluation of tunnels under squeezing rock conditions. The present study confirms the previous findings and contributes additional evidence suggesting that many studies are conducted using empirical and analytical methods to determine the squeezing phenomenon in tunnels. This paper responds to various questions like, what is the squeezing phenomenon? How can we quantify the potential of squeezing in weak rock? What are the different approaches to understanding the squeezing phenomenon?
